'\" et
.TH EXEC "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
exec
\(em execute commands and open, close, or copy file descriptors
.SH SYNOPSIS
.LP
.nf
exec \fB[\fIcommand \fB[\fIargument\fR...\fB]]\fR
.fi
.SH DESCRIPTION
The
.IR exec
utility shall open, close, and/or copy file descriptors as specified by
any redirections as part of the command.
.P
If
.IR exec
is specified without
.IR command
or
.IR argument s,
and any file descriptors with numbers greater than 2 are opened with
associated redirection statements, it is unspecified whether those file
descriptors remain open when the shell invokes another utility.
Scripts concerned that child shells could misuse open file descriptors
can always close them explicitly, as shown in one of the following
examples.
.P
If
.IR exec
is specified with
.IR command ,
it shall replace the shell with
.IR command
without creating a new process. If
.IR argument s
are specified, they shall be arguments to
.IR command .
Redirection affects the current shell execution environment.
.SH OPTIONS
None.
.SH OPERANDS
See the DESCRIPTION.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
None.
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
Not used.
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
If
.IR command
is specified,
.IR exec
shall not return to the shell; rather, the exit status of the process
shall be the exit status of the program implementing
.IR command ,
which overlaid the shell. If
.IR command
is not found, the exit status shall be 127. If
.IR command
is found, but it is not an executable utility, the exit status shall be
126. If a redirection error occurs (see
.IR "Section 2.8.1" ", " "Consequences of Shell Errors"),
the shell shall exit with a value in the range 1\-125. Otherwise,
.IR exec
shall return a zero exit status.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
None.
.SH EXAMPLES
Open
.IR readfile
as file descriptor 3 for reading:
.sp
.RS 4
.nf

exec 3< readfile
.fi
.P
.RE
.P
Open
.IR writefile
as file descriptor 4 for writing:
.sp
.RS 4
.nf

exec 4> writefile
.fi
.P
.RE
.P
Make file descriptor 5 a copy of file descriptor 0:
.sp
.RS 4
.nf

exec 5<&0
.fi
.P
.RE
.P
Close file descriptor 3:
.sp
.RS 4
.nf

exec 3<&-
.fi
.P
.RE
.P
Cat the file
.BR maggie
by replacing the current shell with the
.IR cat
utility:
.sp
.RS 4
.nf

exec cat maggie
.fi
.P
.RE
.SH "RATIONALE"
Most historical implementations were not conformant in that:
.sp
.RS 4
.nf

foo=bar exec cmd
.fi
.P
.RE
.P
did not pass
.BR foo
to
.BR cmd .
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.14" ", " "Special Built-In Utilities"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
